Ann Mullan-Karakatsanis, who does business as Kara Irish Pottery in the United States, has sued Belleek and its US subsidiary in Massachusetts, where she is based.

She has claimed in a complaint filed in court that Belleek has been "palming off" its products as its own despite allegedly using her designs.

The designer moved to Boston in the 1990s and has developed a successful range of products under the 'Aranware' name. The range is manufactured in Ireland and sold here and in the US.

The products have featured on shopping channel QVC, with her company having been supported financially by Invest NI to help develop its US sales.

In publicly available court filings, Ms Mullan-Karakatsanis claims that her trademarked designs on her pottery reflect "unique and distinctive elements of Celtic art and culture".

She claims that in 2008 she approached Belleek in Ireland with a view to sourcing a new manufacturer for her goods. She alleges in her court complaint that Belleek chief executive John Maguire told her the Fermanagh company had little interest in the Aranware collection or its traditional Irish-knit designs.

The designer claims that she forwarded samples of her products to Belleek at the time.

In 2012, she claims she became aware that Belleek was about to launch a range called 'Aran', which was being manufactured in the Far East. While on a visit to Derry, she maintains she met a former Belleek employee who told her that while at Belleek she had been given the US-based designer's brochure and told to mimic the designs.

Ms Mullan-Karakatsanis also claims Belleek was marketing its Aran products as being made in Ireland, when in fact, she alleges, they were being manufactured in the Far East.

The court filing claims that the 'Aran' range being sold by Belleek has been very profitable for the company.

Ms Mullan-Karakatsanis is now seeking damages for the alleged copying of her designs by Belleek.

She has reminded the Massachusetts court that if her action is successful, the court could require that Belleek pay her all profits derived from its sale of products allegedly using her design.

The latest set of accounts for Belleek Pottery show it generated sales of £9m (€10.8m) in the 12 months to the end of March 2013, up 19.3% on the previous year. It broke even in the last financial year.